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High-Current Neutral Electrodes

High-Current Neutral Electrodes DE GRUYTER Current Directions in Biomedical Engineering 2020;6(3): 20203159 Norbert Nessler, Nessler Medizin Elektronik, Innsbruck / AUSTRIA Definition and quality testing of high-current neutral electrodes Abstract: The Standard IEC 60601-2-2:2017 refers to surgeon calls upon this current by activating the electrical neutral electrodes for high current without defining them. scalpel for the (short) activation time t. The energy This paper suggests a practical distinction criterion between standard and high-current neutral electrodes and a E [W s = J] = P [W] * t [s] (1) test procedure. is transformed into heating at the electrical scalpel thus Keywords: Neutral electrodes, high current, long producing the desired surgical effect. The high energy activation time, thermal features, quality test. density evokes local temperatures >100°C so that the tissue cells burst (cut); the effect of temperatures <100°C is https://doi.org/10.1515/cdbme-2020-3159 coagulation (coag). The procedure is visually checked by the surgeon and depends, among other things, on the preselected output P at the ESU and the minute duty cycle of the activation times Introduction t. According to Pearce [2] the minute duty cycle amounts to an average of 15%, max. 45%, which means that current In electrosurgery tissue is cut and coagulated by means of only flows during, on an average, 15% of these activation high-frequency (HF) electrical current. Figure 1 shows the times within every minute. principle setup of a monopolar electrosurgical operation method applying HF output current to a patient via an active electrode and returning this current via a separately- 1.2 Neutral electrode (NE) connected neutral electrode. In monopolar mode the HF current is returned to the ESU via a sufficiently large neutral electrode. Whereas at the active electrode small area of the active electrode high local temperatures are necessary, the heating below the neutral electrode on Active electr the patient must not increase to a dangerous temperature. patient HF-generator The Standard [1] limits this temperature increase to 6°C. current (ESU) The energy E that appears at the transition resistance R neutral electr. between NE and underlying tissue, caused by the current neutral I during the time t is calculated according to Equation (2) NE electrode (NE) as follows: E [J] = (I )² * R * t (2) NE Figure 1: Principle scheme of current flow from the active electrode through the patient’s body to the neutral electrode and The transition resistance R depends not only on size and back to the HF-generator shape of the NE, but also on the morphology and the anatomical properties of the body tissue under the NE. In This operation technique is described in Standard IEC [2] a heating factor hf, independent on R, for the energy per th 60601-2-2, 6 Ed. 2017 [1]. Ohm transition resistance was defined as a measure of the load on the NE as follows: 1.1 Active electrode, electrical scalpel hf = (I )² * t [A² * s] (3) NE The HF generator (ESU) provides the selected output power P [W = V * A ] for the surgical procedure and the eff eff Open Access. © 2020 Norbert Nessler et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. Norbert Nessler et al., High-Current Neutral Electrodes — 2 For adult NEs, the Standard [1] defines a maximum of edges of the active area of the NE, whereas in the center 30A²s for the energy hf and stipulates a temperature test on area the temperature increase is lower. As is shown volunteers or surrogate media or with a testing device with schematically in Fig. 1 and explained in model calculations standard load (700mA during 60s, corresponding to 30A²s) as [3], the current lines concentrate at the edge of the NE with a quality test for NEs. the very edge that is closer to the site of operation showing the highest values, as was to be expected. 1.3 Quality tests with testing device 2 High-current application The test device [3] that was developed at Innsbruck University allows to replace the elaborate tests with thermo The parameters 30A²s standard load and 700mA current cameras at volunteers by electronic measurements. Figure during 60s are the present quality standard for NEs for so- 2 shows a typical such measurement result with the test called conventional operation techniques. Latest surgical device. techniques (ablation), however, apply higher currents and Figure 3 shows a corresponding measurement made with a require longer activation times thus increasing the energy thermo camera on a volunteer. load which can no longer be safely dissipated by means of conventional NEs. 2.1 (Hitherto) distinguishing feature The version of the Standard [1] presently in force defines the load (hf) for NEs in high-current mode (201.3.219) as “above” 30A²s in each 60s interval at maximum output current and maximum duty cycle. The 6°C limit for the maximum temperature increase under the NE remains unchanged. This simply ascertains that conventional NEs Figure. 2: Measurement under standard load with test device are not suited for high-current applications, however, it (electronic skin). Maximum temperature increase is 3,7°C does not indicate any upper limit for the energy load nor a testing procedure for high-current NEs. Furthermore, the specification of maximum output current (201.3.226) led to misinterpretation, since a current above 700mA can also occur for a short time (e.g. during "first cut") in conventional operations. As a result, even ESUs with lower output were classified as high current devices, which means that all NEs would have to belong to the high -current category of accessories. Figure. 3. Reference measurement at volunteer with 2.2 New approach for the thermo camera, Maximum temperature increase is 3,4°C, distinguishing feature (32,4°C to 35,8°C) In the Technical Report [5] a number of surgical procedures The distribution of the temperature increases an the are listed in Chapter 7.5.3 (Surgical procedures utilizing maximum temperatures increases in Figures 2 and 3 are in high currents or long duty cycles) which imply higher load good agreement and thus serve as a “calibration” of the test for the NEs. In all cases a long activation time with a minute device [4] according to Standard [1] item 201.15.101.5. duty cycle of 100% is very probable. A striking feature in both pictures is the so-called „edge effect“: The highest temperature increases appear at the Norbert Nessler et al., High-Current Neutral Electrodes — 3 Instead of distinguishing by energy level (heating factor hf Temperature increase measurements > 30A²s) the new approach for the distinction between on HC-NEs conventional und high-current surgical procedures suggests the activation time that is predetermined by the type of Thermo measurements at the before described NEs with an surgical procedure (ablation). area of 250 cm² (HC-NE250) using currents up to 1,4A and The different distinguishing features between conventional activation times of up to 300s (5 min) are illustrated in and high-current NEs are summarized in Table 1. Figure. 4. Table 1: Differences in activation times between conventional and high-current mode. Conventional High current Heating factor 30A²s Heating factor >30A²s Short activations within Activation time longer than every 60s interval 60s Duty cycle e.g.25% Duty cycle 100% e.g. 15s on, 45s off Activation time several or 60s on, 180s off minutes (ablation) Using the activation time as a distinguishing feature would insure that already in the planning of the surgical procedure the high-current mode is recognized and the correct NEs Figure. 4: Measurements of thermal features of a NE250 under therefore provided already at this stage. high-current load with test device (electronic skin). Green rectangle: see suggestion for a test procedure. 3 Thermal properties of high- Table 2 gives a list of the application field (green cells) of an HC-NE for a maximum temperature increase of 6°C current NEs under the neutral electrode (temperatures in °C). For the currents 500mA and 700mA the observance of the Neutral electrodes for high-current mode (HC-NEs) are 6°C limit can be estimated for activation times up to excluded from the tests 201.15.101.5 (NE thermal 15min by linear extrapolation in the diagram Figure 4. performance) and 201.15.101.9 (Monitoring NEs) described in the Standard [1]. This implies that the thermal Table 2: permissible range for temperature increase up to 6 ° C properties of an HC-NE cannot be tested on volunteers. However, the latest version of the electronic test device [6] \ t 60s 120s 180s 240s 300s 900s*) offers a feature to conduct thermal tests under high-current 1,4 A 4,7 7,1 9,0 conditions. Commercial neutral electrodes for surgery at adult 1,2 A 3,5 5,3 6,7 patients have an active (contact) area between 90 cm² and 1,0 A 2,3 3,5 4,5 5,1 5,5 160 cm² (average value 125 cm²). Since neutral electrodes 0,7A 1,1 1,7 2,0 2,3 2,7 5,5 for high-current surgery are not as yet commercially 0,5A 0,5 0,8 1,1 1,2 1,5 3,2 available in the market such testing of the thermal properties at the electronic test device is conducted with an *) linear extrapolation (15 min) electrode of „suitable size” of 250 cm² (about two times the size of a conventional adult NE). It comes clear from Figure 4 that for currents between 0,5A and 1,0A during 300s no dangerous temperature increase arises. For 1,2A and 1,4A the activations times must not exceed 150s and 90s, respectively and for the Norbert Nessler et al., High-Current Neutral Electrodes — 4 two latter energy loads 2 HC-NEs in parallel as described the present state of the art for HC-NEs. Under this in Figure 5 are recommended. assumption the test procedure for HC-NEs is as follows: Figure 5 shows the temperature increase at each of the two above mentioned HC-NEs in parallel for the indicated total Heating factor hf = 120A²s current. Test with 1.4A during 60s Measuring a HC-NE with thermal properties other than that of the HC-NE250 at 1,4A / 60s on the test device yields a value for the maximum temperature increase (xx°C). If this value is entered in the diagram Figure 4 in the green rectangle (at 60s), the respective temperature curve results directly or can be interpolated. The maximum allowable activation time can then be read from the x-axis If two HC-NEs are used in parallel, use figure 5 instead. Figure. 5: Measurements of thermal features for two HC-NE250 in parallel under high current load. References Due to the new feature in the test device [6] currents up to 1,4A and activations times up to 300s are selectable. [1] IEC 60601-2-2, 6th Ed., 2017, Medical electrical equipment For each combination of parameters as in Figures 4 and 5 – Particular requirements for the basic safety and essential the resulting “thermo pictures” are very similar to those performance of high frequency surgical equipment and high frequency surgical accessories. with conventional NEs, as in Figure 2. [2] PEARCE, JA, GEDDES, LA, VAN VLEET, JF, FOSTER, K, ALLEN, J. Skin burns from electrosurgical current. Medical The measurements in Figure 4 give an indication of a test Instrumentation, 1983, volume 17, number 3, pp. 225-231. procedure that considers activation times of more than 60 [3] Nessler N., Reischer W. Measuring device for neutral seconds. electrodes in electrosurgery, Measurement 33 (2003) pp 197-203, Elsevier Science Ltd., (www.elsevier.com). [4] Nessler N., Reischer W., Salchner M., Calibration of the Electronic Skin, 19th International Metrology Symposium, Proceedings pp 126-128, Opatija, Croatia, 2005. 4 Suggestion for a test [5] IEC TR 61289 Ed2, 2019, High frequency surgical equipment and high frequency surgical accessories - procedure for HC-NEs Operation and maintenance. [6] Nessler N, Salchner M, Niedrist R, Verification of the There is an unpublished information by J. Eggleston [7], thermal properties of the electronic skin, 3-Länder Tagung which forms a preliminary kind of test for HC-NEs and D-A-CH Graz, Proceedings pp 479-480, BMT 2013, [7] unpublished information of Jeffrey L. Eggleston, heating serves as an emergency solution until a final stipulation will factor for high current neutral electrodes, MT17 meeting, be agreed: In analogy to the present quality test during 60s Edinburgh, 2014. with 30A²s, as is requested by the Standard for conventional NEs, a test during 60s with 120A²s at 6°C maximum admissible temperature increase is considered as http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Current Directions in Biomedical Engineering de Gruyter

High-Current Neutral Electrodes

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Abstract

DE GRUYTER Current Directions in Biomedical Engineering 2020;6(3): 20203159 Norbert Nessler, Nessler Medizin Elektronik, Innsbruck / AUSTRIA Definition and quality testing of high-current neutral electrodes Abstract: The Standard IEC 60601-2-2:2017 refers to surgeon calls upon this current by activating the electrical neutral electrodes for high current without defining them. scalpel for the (short) activation time t. The energy This paper suggests a practical distinction criterion between standard and high-current neutral electrodes and a E [W s = J] = P [W] * t [s] (1) test procedure. is transformed into heating at the electrical scalpel thus Keywords: Neutral electrodes, high current, long producing the desired surgical effect. The high energy activation time, thermal features, quality test. density evokes local temperatures >100°C so that the tissue cells burst (cut); the effect of temperatures <100°C is https://doi.org/10.1515/cdbme-2020-3159 coagulation (coag). The procedure is visually checked by the surgeon and depends, among other things, on the preselected output P at the ESU and the minute duty cycle of the activation times Introduction t. According to Pearce [2] the minute duty cycle amounts to an average of 15%, max. 45%, which means that current In electrosurgery tissue is cut and coagulated by means of only flows during, on an average, 15% of these activation high-frequency (HF) electrical current. Figure 1 shows the times within every minute. principle setup of a monopolar electrosurgical operation method applying HF output current to a patient via an active electrode and returning this current via a separately- 1.2 Neutral electrode (NE) connected neutral electrode. In monopolar mode the HF current is returned to the ESU via a sufficiently large neutral electrode. Whereas at the active electrode small area of the active electrode high local temperatures are necessary, the heating below the neutral electrode on Active electr the patient must not increase to a dangerous temperature. patient HF-generator The Standard [1] limits this temperature increase to 6°C. current (ESU) The energy E that appears at the transition resistance R neutral electr. between NE and underlying tissue, caused by the current neutral I during the time t is calculated according to Equation (2) NE electrode (NE) as follows: E [J] = (I )² * R * t (2) NE Figure 1: Principle scheme of current flow from the active electrode through the patient’s body to the neutral electrode and The transition resistance R depends not only on size and back to the HF-generator shape of the NE, but also on the morphology and the anatomical properties of the body tissue under the NE. In This operation technique is described in Standard IEC [2] a heating factor hf, independent on R, for the energy per th 60601-2-2, 6 Ed. 2017 [1]. Ohm transition resistance was defined as a measure of the load on the NE as follows: 1.1 Active electrode, electrical scalpel hf = (I )² * t [A² * s] (3) NE The HF generator (ESU) provides the selected output power P [W = V * A ] for the surgical procedure and the eff eff Open Access. © 2020 Norbert Nessler et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. Norbert Nessler et al., High-Current Neutral Electrodes — 2 For adult NEs, the Standard [1] defines a maximum of edges of the active area of the NE, whereas in the center 30A²s for the energy hf and stipulates a temperature test on area the temperature increase is lower. As is shown volunteers or surrogate media or with a testing device with schematically in Fig. 1 and explained in model calculations standard load (700mA during 60s, corresponding to 30A²s) as [3], the current lines concentrate at the edge of the NE with a quality test for NEs. the very edge that is closer to the site of operation showing the highest values, as was to be expected. 1.3 Quality tests with testing device 2 High-current application The test device [3] that was developed at Innsbruck University allows to replace the elaborate tests with thermo The parameters 30A²s standard load and 700mA current cameras at volunteers by electronic measurements. Figure during 60s are the present quality standard for NEs for so- 2 shows a typical such measurement result with the test called conventional operation techniques. Latest surgical device. techniques (ablation), however, apply higher currents and Figure 3 shows a corresponding measurement made with a require longer activation times thus increasing the energy thermo camera on a volunteer. load which can no longer be safely dissipated by means of conventional NEs. 2.1 (Hitherto) distinguishing feature The version of the Standard [1] presently in force defines the load (hf) for NEs in high-current mode (201.3.219) as “above” 30A²s in each 60s interval at maximum output current and maximum duty cycle. The 6°C limit for the maximum temperature increase under the NE remains unchanged. This simply ascertains that conventional NEs Figure. 2: Measurement under standard load with test device are not suited for high-current applications, however, it (electronic skin). Maximum temperature increase is 3,7°C does not indicate any upper limit for the energy load nor a testing procedure for high-current NEs. Furthermore, the specification of maximum output current (201.3.226) led to misinterpretation, since a current above 700mA can also occur for a short time (e.g. during "first cut") in conventional operations. As a result, even ESUs with lower output were classified as high current devices, which means that all NEs would have to belong to the high -current category of accessories. Figure. 3. Reference measurement at volunteer with 2.2 New approach for the thermo camera, Maximum temperature increase is 3,4°C, distinguishing feature (32,4°C to 35,8°C) In the Technical Report [5] a number of surgical procedures The distribution of the temperature increases an the are listed in Chapter 7.5.3 (Surgical procedures utilizing maximum temperatures increases in Figures 2 and 3 are in high currents or long duty cycles) which imply higher load good agreement and thus serve as a “calibration” of the test for the NEs. In all cases a long activation time with a minute device [4] according to Standard [1] item 201.15.101.5. duty cycle of 100% is very probable. A striking feature in both pictures is the so-called „edge effect“: The highest temperature increases appear at the Norbert Nessler et al., High-Current Neutral Electrodes — 3 Instead of distinguishing by energy level (heating factor hf Temperature increase measurements > 30A²s) the new approach for the distinction between on HC-NEs conventional und high-current surgical procedures suggests the activation time that is predetermined by the type of Thermo measurements at the before described NEs with an surgical procedure (ablation). area of 250 cm² (HC-NE250) using currents up to 1,4A and The different distinguishing features between conventional activation times of up to 300s (5 min) are illustrated in and high-current NEs are summarized in Table 1. Figure. 4. Table 1: Differences in activation times between conventional and high-current mode. Conventional High current Heating factor 30A²s Heating factor >30A²s Short activations within Activation time longer than every 60s interval 60s Duty cycle e.g.25% Duty cycle 100% e.g. 15s on, 45s off Activation time several or 60s on, 180s off minutes (ablation) Using the activation time as a distinguishing feature would insure that already in the planning of the surgical procedure the high-current mode is recognized and the correct NEs Figure. 4: Measurements of thermal features of a NE250 under therefore provided already at this stage. high-current load with test device (electronic skin). Green rectangle: see suggestion for a test procedure. 3 Thermal properties of high- Table 2 gives a list of the application field (green cells) of an HC-NE for a maximum temperature increase of 6°C current NEs under the neutral electrode (temperatures in °C). For the currents 500mA and 700mA the observance of the Neutral electrodes for high-current mode (HC-NEs) are 6°C limit can be estimated for activation times up to excluded from the tests 201.15.101.5 (NE thermal 15min by linear extrapolation in the diagram Figure 4. performance) and 201.15.101.9 (Monitoring NEs) described in the Standard [1]. This implies that the thermal Table 2: permissible range for temperature increase up to 6 ° C properties of an HC-NE cannot be tested on volunteers. However, the latest version of the electronic test device [6] \ t 60s 120s 180s 240s 300s 900s*) offers a feature to conduct thermal tests under high-current 1,4 A 4,7 7,1 9,0 conditions. Commercial neutral electrodes for surgery at adult 1,2 A 3,5 5,3 6,7 patients have an active (contact) area between 90 cm² and 1,0 A 2,3 3,5 4,5 5,1 5,5 160 cm² (average value 125 cm²). Since neutral electrodes 0,7A 1,1 1,7 2,0 2,3 2,7 5,5 for high-current surgery are not as yet commercially 0,5A 0,5 0,8 1,1 1,2 1,5 3,2 available in the market such testing of the thermal properties at the electronic test device is conducted with an *) linear extrapolation (15 min) electrode of „suitable size” of 250 cm² (about two times the size of a conventional adult NE). It comes clear from Figure 4 that for currents between 0,5A and 1,0A during 300s no dangerous temperature increase arises. For 1,2A and 1,4A the activations times must not exceed 150s and 90s, respectively and for the Norbert Nessler et al., High-Current Neutral Electrodes — 4 two latter energy loads 2 HC-NEs in parallel as described the present state of the art for HC-NEs. Under this in Figure 5 are recommended. assumption the test procedure for HC-NEs is as follows: Figure 5 shows the temperature increase at each of the two above mentioned HC-NEs in parallel for the indicated total Heating factor hf = 120A²s current. Test with 1.4A during 60s Measuring a HC-NE with thermal properties other than that of the HC-NE250 at 1,4A / 60s on the test device yields a value for the maximum temperature increase (xx°C). If this value is entered in the diagram Figure 4 in the green rectangle (at 60s), the respective temperature curve results directly or can be interpolated. The maximum allowable activation time can then be read from the x-axis If two HC-NEs are used in parallel, use figure 5 instead. Figure. 5: Measurements of thermal features for two HC-NE250 in parallel under high current load. References Due to the new feature in the test device [6] currents up to 1,4A and activations times up to 300s are selectable. [1] IEC 60601-2-2, 6th Ed., 2017, Medical electrical equipment For each combination of parameters as in Figures 4 and 5 – Particular requirements for the basic safety and essential the resulting “thermo pictures” are very similar to those performance of high frequency surgical equipment and high frequency surgical accessories. with conventional NEs, as in Figure 2. [2] PEARCE, JA, GEDDES, LA, VAN VLEET, JF, FOSTER, K, ALLEN, J. Skin burns from electrosurgical current. Medical The measurements in Figure 4 give an indication of a test Instrumentation, 1983, volume 17, number 3, pp. 225-231. procedure that considers activation times of more than 60 [3] Nessler N., Reischer W. Measuring device for neutral seconds. electrodes in electrosurgery, Measurement 33 (2003) pp 197-203, Elsevier Science Ltd., (www.elsevier.com). [4] Nessler N., Reischer W., Salchner M., Calibration of the Electronic Skin, 19th International Metrology Symposium, Proceedings pp 126-128, Opatija, Croatia, 2005. 4 Suggestion for a test [5] IEC TR 61289 Ed2, 2019, High frequency surgical equipment and high frequency surgical accessories - procedure for HC-NEs Operation and maintenance. [6] Nessler N, Salchner M, Niedrist R, Verification of the There is an unpublished information by J. Eggleston [7], thermal properties of the electronic skin, 3-Länder Tagung which forms a preliminary kind of test for HC-NEs and D-A-CH Graz, Proceedings pp 479-480, BMT 2013, [7] unpublished information of Jeffrey L. Eggleston, heating serves as an emergency solution until a final stipulation will factor for high current neutral electrodes, MT17 meeting, be agreed: In analogy to the present quality test during 60s Edinburgh, 2014. with 30A²s, as is requested by the Standard for conventional NEs, a test during 60s with 120A²s at 6°C maximum admissible temperature increase is considered as

Journal

Current Directions in Biomedical Engineering – de Gruyter

Published: Sep 1, 2020

Keywords: Neutral electrodes; high current; long activation time; thermal features; quality test

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